U.S. officials have complained about poor cooperation with governments in region

The FBI director met with top Libyan officials on Thursday to discuss the probe into last year’s killing of the U.S. ambassador in Benghazi where authorities are planning a curfew following an upsurge in violence, Libyan officials said.

Ambassador Chris Stevens and three other Americans, including Glen Doherty of Encinitas and Tyrone Woods of Imperial Beach, were killed on Sept. 11, 2012, in an attack that Washington officials suspect was carried out by militants linked to the al-Qaeda terrorist group. There has been little news of progress in the investigation, and U.S. officials have complained about poor cooperation with governments in the region.

The officials, who spoke on condition of anonymity because of the sensitive nature of the visit, said FBI Director Robert Mueller discussed the case in Tripoli with senior officials, including the prime minister, justice minister and intelligence chief.

U.S. officials have not announced the capture of any suspects in the attack, although President Barack Obama said in December that investigators have some “very good leads.”

Obama, in a speech the day after the attack, said he would “work with the Libyan government to bring to justice the killers who attacked our people.”

The security of the U.S. diplomatic sites in Benghazi has become a political flash point for the Obama administration. A Senate report in December said the State Department did not focus tightly enough on Libyan extremists or react quickly enough to threat assessments in the weeks before the attack.

Secretary of State Hillary Clinton is scheduled to discuss the attack with two congressional committees on Jan. 23.

It is unclear when Libyan authorities plan to impose a curfew following a string of deadly attacks, assassinations of top security officials and other unrest in recent months. Libyan Prime Minister Ali Zidan said on Wednesday that 18,000 new police recruits would be dispatched to the city in an effort to enforce the curfew.

Interior Minister Ashour Shaweil told reporters that when it starts, it will be enforced for five hours every night beginning at midnight. Several check points will be installed around the city, he said.

Authorities in Libya have been struggling to form unified army and police force since 2011 when former Libyan dictator Moammar Gadhafi was ousted and killed in a mass uprising that turned to armed conflict when citizens raised arms against Gadhafi’s forces.

In recent months, there has been a series of assassinations of top security officials and bombings of security headquarters in the northeastern city of Benghazi. Some blame Islamist extremists, but residents suspect more than one group is involved and that some of the violence is being carried out by those who have personal vendettas against officials who once served in Gadhafi’s police force.